Conventional spin-on filter designs use a thread plate at the interface end of the filter assembly. This thread plate has flow passages to allow flow in and out of the filter assembly. In addition, there is often an attaching feature near the center line of the filter assembly where threads on the thread plate engage threads on the filter head.
An alternate design is what is sometimes referred to as a “big mouth” filter. In such “big mouth” filters, the thread plate is replaced with a threaded ring. The attaching feature is near the outside diameter of the filter assembly. This design reduces the overall amount of material and is structurally stronger than the thread plate design. The big mouth design has the flexibility of using either internal or external threads. Internal threads are typically used on applications that accept either a spin-on or a bowl/cartridge design. The threaded ring mentioned above, uses internal threads.
Using external threads for a spin-on filter presents technical issues because the typical seaming process used with a threaded ring can not be used. Improvements are desirable.